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| Titel |
Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings |
| VerfasserIn |
H. Wex, P. J. DeMott, Y. Tobo, S. Hartmann, M. Rösch, T. Clauss, L. Tomsche, D. Niedermeier, F. Stratmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 11 ; Nr. 14, no. 11 (2014-06-04), S.5529-5546 |
| Datensatznummer |
250118772
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| Publikation (Nr.) |
 copernicus.org/acp-14-5529-2014.pdf |
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| Zusammenfassung |
Kaolinite particles from two different sources (Fluka and Clay
Minerals Society (CMS)) were examined with respect to their ability
to act as ice nuclei (IN). This was done in the water-subsaturated regime
where often deposition ice nucleation is assumed to occur, and for
water-supersaturated conditions, i.e., in the immersion freezing
mode. Measurements were done using a flow tube (the Leipzig Aerosol Cloud Interaction Simulator, LACIS) and
a continuous-flow diffusion chamber (CFDC). Pure and coated
particles were used, with coating thicknesses of a few nanometers or
less, where the coating consisted of levoglucosan, succinic
acid or sulfuric acid. In general, it was found that the coatings
strongly reduced deposition ice nucleation. Remaining ice formation
in the water-subsaturated regime could be attributed to immersion
freezing, with particles immersed in concentrated solutions formed
by the coatings.
In the immersion freezing mode, ice nucleation rate coefficients
jhet from both instruments agreed well with each other, particularly when
the residence times in the instruments were accounted for. Fluka
kaolinite particles coated with either levoglucosan or succinic acid
showed the same IN activity as pure Fluka kaolinite particles;
i.e., it can be assumed that these two types of coating did not alter
the ice-active surface chemically, and that the coatings were
diluted enough in the droplets that were formed prior to the ice
nucleation, so that freezing point depression was
negligible. However, Fluka kaolinite particles, which were either coated
with pure sulfuric acid or were first coated with the
acid and then exposed to additional water vapor, both showed
a reduced ability to nucleate ice compared to the pure
particles. For the CMS kaolinite particles, the ability to nucleate
ice in the immersion freezing mode was similar for all examined
particles, i.e., for the pure ones and the ones with the different
types of coating. Moreover, jhet derived for the CMS
kaolinite particles was comparable to jhet derived for
Fluka kaolinite particles coated with sulfuric acid. This is suggestive
for the Fluka kaolinite possessing a type of ice-nucleating surface
feature which is not present on the CMS kaolinite, and which can be
destroyed by reaction with sulfuric acid. This might be potassium
feldspar. |
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